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=============================================================================
FreeBSD-SA-98:03                                            Security Advisory
                                                                FreeBSD, Inc.

Topic:          Problems with TTCP

Category:       core
Module:         kernel
Announced:      1998-05-14, revised at 1998-05-18
Affects:        FreeBSD 2.1.*
		FreeBSD 2.2.*,
		FreeBSD-2.2-stable before 1998/05/14 and
		FreeBSD-3.0-current before 1998/05/05 suffer from this problem.
Corrected:      FreeBSD-3.0-current as of 1998/05/14
		FreeBSD-2.2-stable as of 1998/05/05
		FreeBSD-2.1-stable as of 1998/05/18
FreeBSD only:   No. Any other system incorporating TTCP extentions may be
                affected.

Patches:        ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:03/

I.   Background    


     RFC 1644 provides an extension to TCP called TCP Extensions for
     Transactions, or shortly T/TCP. It provides a way of bypassing
     the standard three-way handshake found in TCP, thus speeding up
     transactions.
     T/TCP has been incorporated in FreeBSD since FreeBSD 2.0.5.

II.  Problem Description

     An accelerated open is initiated by a client by sending a new
     TCP option, called CC, to the server.  The kernel keeps a
     special cache for each host it communicated with, among others
     containing the value of the last CC option used by the client.
     A new accelerated open is allowed when the CC sent is larger
     than the one in the per-host cache. Thus one can spoof complete
     connections.
     
III. Impact
     
     The hole can be used to obtain unauthorized acces to the system
     by spoofing connections to the r*-services. This can only be
     done in the case where an .rhost file and/or a host.equiv file
     is used as the sole method of authentication.

IV.  Workaround

     Disable all r-* services. Note that setting the kernel variable
     net.inet.tcp.rfc1644 to 0 does not solve the problem. This
     variable controls whether the system will initiate rfc1644
     based connections and does not affect the ability to receive
     such connections.

V.   Solution


     Apply the following patch, rebuild your kernel, install it
     and reboot your system. The patch is valid for 2.1.* systems,
     for 2.1-stable, for 2.2.* systems, for 2.2-stable and for 3.0-current.

     The patch below can be found on
	ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:03/

   
  Index: tcp_input.c
  ===================================================================
  RCS file: /home/ncvs/src/sys/netinet/tcp_input.c,v
  retrieving revision 1.74
  retrieving revision 1.77
  diff -u -r1.74 -r1.77
  --- tcp_input.c	1998/04/24 10:08:57	1.74
  +++ tcp_input.c	1998/05/18 17:11:24	1.77
  @@ -680,7 +680,9 @@
   		 * - otherwise do a normal 3-way handshake.
   		 */
   		if ((to.to_flag & TOF_CC) != 0) {
  -		    if (taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
  +		    if (((tp->t_flags & TF_NOPUSH) != 0) &&
  +			taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
  +
   			taop->tao_cc = to.to_cc;
   			tp->t_state = TCPS_ESTABLISHED;
   
    
    
=============================================================================
FreeBSD, Inc.

Web Site:                       http://www.freebsd.org/
Confidential contacts:          security-officer@freebsd.org
Security notifications:         security-notifications@freebsd.org
Security public discussion:     freebsd-security@freebsd.org
PGP Key:                ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc

Notice: Any patches in this document may not apply cleanly due to
        modifications caused by digital signature or mailer software.
        Please reference the URL listed at the top of this document
        for original copies of all patches if necessary.
=========================================================================

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